In general this invention relates to the positioning of a blade mechanism and, more particularly, to the magnetic positioning of a blade mechanism.
Focusing systems are known in which an optical lens element changes its distance to a focal plane in accordance with the object distance. Commonly-assigned U.S. Pat. No. 3,902,792 describes one such system.
Problems are associated with these focusing systems when used with simple lenses of the fixed-focus type. These problems are normally overcome by maintaining a fixed spatial relationship between the aperture stop and the meniscus lens element of the focusing system. Maintaining such a fixed relationship is relatively easy to obtain when the meniscus lens element and the aperture stop can be moved as a unit.
However, when a shutter is introduced into such an arrangement, the situation becomes somewhat complicated. This is because the aperture associated with the shutter may interfere with the stop's function in correcting coma aberration or actually take over its function if proper precautions are not exercised. There are a number of proposals for solving such complications.
One provides a stationary shutter whose aperture is sufficiently large so that it never becomes part of the optical system or interferes with a coma correcting stop. In this manner, the lens may be focused without degradation in image quality, but the shutter must, in general, be relatively large and probably relatively expensive, as, for example, a focal plane type.
Another solution involves moving the entire shutter assembly with the lens to maintain some fixed shutter-to-lens distance as the lens is focused. This is a well-known approach used in folding type cameras. Commonly-assigned U.S. Pat. Nos. 3,185,060 and 3,087,400 are illustrative of this type of proposal. Commonly-assigned U.S. Pat. No. 3,902,792 discloses structure for maintaining such a spatial relationship in a rigid body type camera. These foregoing approaches have been considered less than entirely satisfactory because they add to camera size and require that the entire shutter be moved in concert with the lens. U.S. Pat. No. 4,130,357 shows a flexible shutter which moves with the lens and must possess predetermined flexing characteristics, as well as a relatively complicated blade guide and blade coupling arrangement.